In a cataract operation, a cornea and a sclera are incised with a width corresponding to a dimension of a lens to be embedded for embedding the lens in an eyeball. As the medical knife used when incising the eyeball, there is one of which planar shape is formed into a substantially rhombic shape. Such medical knife has a sharp tip, a cutting part having two edges radially formed from the tip, a maximum-width part in which a width dimension of the cutting part is the largest, and a shank part continuously formed from the maximum-width part of which width dimension decreases as is away from the maximum-width part (for example, refer to Patent Document 1).
In a case of the above-described medical knife, by allowing the same to straightly penetrate the eyeball, an incision corresponding to the dimension of the maximum-width part may be formed. Especially, in the medical knife disclosed in Patent Document 1, durability of the sharp tip may be improved, and since the edges are formed on both sides from the maximum-width part to the shank part, the penetration resistance may be made small.
In the medical knife disclosed in Patent Document 1, the edges are formed on the both sides in the maximum-width part and the edges are formed also from the maximum-width part to the shank part. Therefore, high incision performance to the tissue is maintained of course from the tip to the maximum-width part and even after the maximum-width part passes through the tissue.
Therefore, the penetration resistance generated when incising the eyeball with the above-described medical knife is a substantially similar small value from the tip to the maximum-width part and the substantially similar penetration resistance is maintained even after the maximum-width part passes through the tissue. When the maximum-width part passes through the tissue and the width of the knife decreases toward the shank, the penetration resistance drastically decreases.
Patent Document 1: Japanese Patent No. 4161026